Sextant (sext)

General & non-SICurrent unit

One sixth of a full turn (60 degrees), named after the navigation instrument whose arc spans a sixth of a circle.

1 sextant = 0.1666666667 turns (approximately).

About the sextant

The name sextant comes from the Latin for one sixth, and the instrument's frame is a sector of roughly 60 degrees, a sixth of a circle. Double reflection lets its scale read up to 120 degrees, enough for lunar distance measurements, which can exceed 90 degrees. John Hadley and Thomas Godfrey implemented the principle around 1731, and Isaac Newton's unpublished writings contain it as well. Navigators mainly use the sextant to measure the height of the Sun or a star above the horizon, from which latitude can be estimated.

It needs no electricity or satellite signal, so it still serves as a backup. The best accuracy possible in celestial navigation is about 0.1 nautical mile, and a highly skilled navigator can reach roughly 0.25. Buzz Aldrin used one on Gemini XII in 1966, and Carlos Viegas Gago Coutinho adapted it for aviation in 1922. As a unit of angle, a sextant is simply 60 degrees: 1/6 of a turn, or π/3 radian.

Sources: Wikipedia: Sextant; Wikipedia: Octant (instrument)

Sextant conversion chart

1 sextant expressed in every other angle unit:

More General & non-SI units

• degree (angle)
• gradian (angle)
• turn (angle)
• arcminute (angle)
• arcsecond (angle)
• right angle (angle)
• octant (angle)
• piece (counting & quantity)
• pair (counting & quantity)
• score (counting & quantity)
• hundred (counting & quantity)
• thousand (counting & quantity)
• million (counting & quantity)
• billion (short scale) (counting & quantity)
• trillion (short scale) (counting & quantity)
• billion (long scale) (counting & quantity)

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